out of memory during startup

i am using mysql 5.0.45 on an server with 4GB RAM,
OS is NetBSD, only MyISAM Tables.

During startup of the mysql-server 1 get this warnings in the error-log:
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095021 11:50:34 mysqld started
/usr/pkg/libexec/mysqld: Out of memory (Needed 475054080 bytes)
/usr/pkg/libexec/mysqld: Out of memory (Needed 356290560 bytes)
/usr/pkg/libexec/mysqld: Out of memory (Needed 267217920 bytes)
/usr/pkg/libexec/mysqld: Out of memory (Needed 200411136 bytes)
/usr/pkg/libexec/mysqld: Out of memory (Needed 150306816 bytes)
/usr/pkg/libexec/mysqld: Out of memory (Needed 112730112 bytes)
090121 11:50:34 [Note] /usr/pkg/libexec/mysqld: ready for connections.
___________________________

This depends on the value of the key_buffer size.
I get this warning if the key_buffer set greater than 96M.

But this value seems a little bit low. There is running an huge typo3-Site.

Upgrading to version 5.0.67 gives the same and additonal warings:
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095619 17:56:43 Starting mysqld daemon with databases from /var/mysql
095619 17:56:43 mysqld started